Hexanchidae, Gray, 1851

Szabó, Márton, 2017, Fish remains from the Lower Cretaceous (Valanginian-Hauterivian) of Hárskút (Hungary, Bakony Mts), Fragmenta Palaeontologica Hungarica 34, pp. 49-61 : 53-54

Hexanchidae indet.

( Figs 7–8 )

Referred material – 1 lower tooth (MBFSZ 2017.237.1.); stratigraphic origin: Valanginian (HK-12/8) .

Description – Only the crown is preserved, the full root is missing. The crown is embedded in a small piece of limestone, where it is displayed in lingual aspect. The preserved crown seems to be incomplete both mesially and distally; therefore the exact number of the mesial and distal cusplets can not be given. The crown is mesiodistally long, while apicobasally low, which refers to a possible lower tooth. Two, distally curved mesial cusplets are preserved. They distally increase in size, the mesial cutting edge of the first mesial cusplet is straight, while that of the second one is convex. The distal cutting edge of both mesial cusplets is weakly convex. The main cusp and the two distal cusplets are distally inclined, they show a characteristic, sigmoid contour (see on Fig. 8 ). This sigmoidism is given by the asymmetric convexity of their mesial cutting edge, and the weak convexity of their distal cutting edge. The preserved mesial and distal cusplets are nearly equal in size; however, the mesials are still smaller.

Remarks – Family Hexanchidae is the most abundant hexanchoid family, ranges from the Mesozoic to the Recent ( CAPPETTA 2012). The Hárskút hexanchid specimen is reminiscent of the teeth of Notidanodon , a hexanchid genus, which was also present in the Lower Cretaceous ( CAPPETTA 2012; MUTTERLOSE 1984; THIES 1987; WARD & THIES 1987), however, since the tooth is too poorly preserved, here I describe it only as Hexanchidae indet.

Figures

Figs 7–8. Hexanchidae indet. lower tooth (MBFSZ 2017.237.1.) from bed HK-12/8 (Valanginian). – 7. Lingual view. – 8. Line drawing of the same specimen, for showing the sigmoidity of the acrocone and accessory conules. – Figs 9–11. Sphenodus sp. (MBFSZ 2017.245.1.) from the uppermost (Hauterivian) part of the HK-12 section. – 9. Lingual view. – 10. Profile view. – 11. Labial view. – Fig. 12. Sphenodus sp. tooth (MBFSZ 2017.238.1.) from bed HK-12/10 (Valanginian),?lingual view. – Figs 13–15. Sphenodus sp. tooth (MBFSZ 2017.241.1.) from bed HK-12/10 (Valanginian). – 13. Lingual view. – 14. Profile view.– 15. Labial view. – Figs 16–17. Lepidotes sp. tooth (MBFSZ 2017.246.1.) from the uppermost (Hauterivian) part of the HK-12 section. – 16. Profile view. – 17. Occlusal view. – Figs 18–20. Gyrodus sp. tooth (MBFSZ 2017.247.1.) from bed HK-12/9 (Valanginian), in three different views showing the occlusal surface